1. Field of the Invention
The present invention relates to a magneto-optical recording medium which is applied to a disk memory for a computer, a reloadable optical memory for document filing or the like.
2. Description of the Prior Art
It is known that materials for the aforementioned magneto-optical recording purposes must mainly satisfy in practice the following conditions:
(i) the magnetization should be oriented vertically to a film surface;
(ii) the Curie temperature should be within a range of 100.degree. C. to 200.degree. C.;
(iii) the medium should have a large coercive force; and
(iv) the value of .sqroot.R..theta.k should be large, assuming that R represents a reflection factor and .theta.k represents Kerr's angle of rotation.
It is well known that when rare earth elements such as Gd and Tb are added to Fe, the magnetic anisotropic energy is increased to form a vertical magnetic anisotropic film. Thus, a thin film of an amorphous alloy, mainly composed of Tb, Fe and Co has been put into practice as the material for a magneto-optical recording medium. Examples of such thin films are those of GdTbFe, TbFeCo, GdTbFeCo and the like.
These conventional thin amorphous alloy films satisfy all of the aforementioned conditions.
However, Tb, which is an important component of the aforementioned thin amorphous alloy films, is one of the scarcest materials of the rare earth elements. Thus, it is desirable to develop a thin amorphous alloy film not containing any Tb, yet which can serve equally as well as those containing Tb, such as GdTbFe, TbFeCo and GdTbFeCo. Clark numbers of principal rare earth elements are as follows:
Gd: 6.times.10.sup.-4 PA0 Nd: 2.2.times.10.sup.-3 PA0 Sm: 6.times.10.sup.-4 PA0 Dy: 4.times.10.sup.-4 PA0 Ho: 1.times.10.sup.-4 PA0 Tb: 8.times.10.sup.-5
In the aforementioned point of view, amorphous magneto-optical recording media employing no Tb have been developed in recent years. For example, Gd--Fe satisfies the aforementioned conditions except for the required coercive force, and hence Sm is is added to Gd--Fe to increase the coercive force (Japan Institute of Applied Magnetics, seventh meeting summary p. 193).
However, Gd--Sm--Fe is small in vertical magnetic anisotropy, and an effective recording medium cannot be obtained by the same.